-
[show abstract]
[hide abstract]
ABSTRACT: The aggregation behaviors of a series of dissymmetric cationic Gemini surfactants, [CmH2m+1(CH3)2N(CH2)2N(CH3)2CnH2n+1]Br2, designated as m-2-n (with a fixed m + n = 24, m = 16, 14, 12) have been investigated in a protic ionic liquid, ethylammonium nitrate (EAN). Surface tension, polarized optical microscopy (POM), small-angle X-ray scattering (SAXS) and rheological measurements are adopted to investigate the micellization and lyotropic liquid crystal (LLC) formation. The obtained results indicate that the structure dissymmetry plays an important role in aggregation process of m-2-n. With increasing the dissymmetry degree, the critical micellization concentration, the maximum reduction of solvent surface tension, and the minimum area occupied per surfactant molecule at the air/EAN interface all become smaller. The thermostability of formed LLCs is therefore improved because of the more compacted molecules. These characteristics can be explained by the enhancement of solvophobic effect due to the increased structure dissymmetry of Gemini surfactants.
Langmuir 11/2012; · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The lyotropic liquid crystalline (LLC) phases formed by a series of N-alkyl-N-methylpiperidinium bromides (C(n)PDB, n=12, 14, 16) in water have been investigated. By using polarized optical microscopy (POM) and small angle X-ray scattering (SAXS) techniques, the normal hexagonal (H(1)) and reverse bicontinuous cubic (V(2)) LLC phases can be detected with C(14)PDB/H(2)O and C(16)PDB/H(2)O systems within a large temperature and concentration ranges. In the C(12)PDB/H(2)O system, only the H(1) phase is observed. Such differences may be attributed to differences in hydrophobic interactions resulting from their different alkyl chain lengths. The rheological results reveal that the H(1) phase formed by C(12)PDB displays a typical Maxwell behavior, whereas those with C(14)PDB or C(16)PDB show gel-like behavior, unlike the traditional cationic surfactants. The obtained results on the LLC phases formed by this new class of piperidinium surfactants supplement the current understanding about nitrogen-containing heterocyclic headgroup-based cationic surfactants and may open their wide potential applications.
Journal of Colloid and Interface Science 09/2012; 389(1):199-205. · 3.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The aggregation behaviors of three Gemini surfactants [(C(s)H(2s)-α,ω-(Me(2)N(+)C(m)H(2m+1)Br(-))(2), s = 2, m = 10, 12, 14] in a protic ionic liquid, ethylammonium nitrate (EAN), have been investigated. The polarized optical microscopy and small-angle X-ray scattering (SAXS) measurements are used to explore the lyotropic liquid crystal (LLC) formation. Compared to the LLCs formed in aqueous environment, the normal hexagonal and lamellar phases disappear. However, with increasing the surfactant concentration, a new reverse hexagonal phase (H(II)) can be mapped over a large temperature range except for other ordered aggregates including the isotropic solution phase and a two-phase coexistence region. The structural parameters of the H(II) are calculated from the corresponding SAXS patterns, showing the influence of surfactant amount, alkyl chain length, and temperature. Meanwhile, the rheological profiles indicate a typical Maxwell behavior of the LLC phases formed in EAN.
Langmuir 12/2011; 28(5):2476-84. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Wormlike nanowires have been successfully prepared via the ionic self-assembly (ISA) route from the cationic (ferrocenylmethyl)trimethylammonium iodide (FcMI) and the anionic sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT). The formed FcM-AOT complexes have been proved to possess a composition of equal molar ratio and show good redox activity also due to the introduction of organic metal ferrocene. These complexes exhibit an ordered hexagonal columnar structure with the lattice spacing D of 2.49 nm. More interestingly, the wormlike nanowires interweave themselves together to form a net-like structure, and some of them are large enough to exhibit a high-order crystal structure. In addition, such an ISA organized aggregate can be changed into vesicles by including the Fc blocks into beta-cyclodextrins to form another supramolecular complex. The supramolecular structure and morphology of the vesicles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. Both the complex fabrication and transition mechanisms are discussed and found to be controlled by the inclusion equilibrium and the cooperative binding of noncovalent interactions, including the electrostatic interactions, pi-pi stacking, and amphiphilic hydrophobic association.
The Journal of Physical Chemistry B 08/2010; 114(32):10384-90. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The aggregation behaviors of oleyl polyoxyethylene (10) ether, Brij 97, in room temperature ionic liquids, ethylammonium nitrate (EAN), pyrrolidinium nitrate ([Pyrr][NO(3)]), ethylammonium butyrate (EAB), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF(6)]), and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), have been investigated. Only in the Brij 97/EAN binary system is the hexagonal liquid crystalline phase formed, and its ordering is found to decrease with increasing temperature. The lattice spacing values measured from the small-angle X-ray scattering (SAXS) shrink with reduction of ionic liquid content at room temperature. The general rules for aggregate formation in these ionic liquids are discussed and compared with that in water. A degraded ability to produce the ordered self-assembly of Brij 97 from H(2)O to EAN to [Bmim][PF(6)], [Bmim][BF(4)], [Pyrr][NO(3)], and EAB is found and analyzed based on the molecular packing and Gordon parameters and also hydrogen-bonding or solvophobic interactions. Steady-shear rheological measurements combined with the frequency sweep data indicate the highly viscoelastic nature of this liquid crystalline phase.
Langmuir 06/2010; 26(11):7802-7. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The phase behavior of a catanionic system composed by a cationic surfactive ionic liquid (IL), 1-hexadecyl-3-methylimidazolium chloride ([C(16)mim]Cl), an anionic sodium dodecyl sulfate (SDS), and water has been investigated. A novel gel phase with quite high water content can be fabricated showing similar rheological properties to vesicles usually formed in traditional catanionic systems. The lamellar structure could also be constructed in SDS-rich region. Both the hydrophobic interaction of alkyl chains and interactions between oppositely charged head groups play important roles for the gel formation. Such a facile method to form gels directly from the catanionic system at relative low surfactant concentrations is novel, which should be related to the specific molecular structure of imidazolium ILs. The obtained results are expected to be helpful for better understanding of catanionic systems.
The Journal of Physical Chemistry B 02/2009; 113(4):983-8. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The aggregation behavior of a surfactant-like ionic liquid, 1-hexadecyl-3-methylimidazolium chloride (C(16)mimCl), in a room temperature ionic liquid ethylammonium nitrate (EAN) has been investigated. With increasing C(16)mimCl concentration, a series of ordered aggregates including micelles, normal hexagonal (H(1)), lamellar (L(alpha)), and reverse bicontinuous cubic (V(2)) liquid crystalline (LC) phases can be detected over a large temperature range by using polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) techniques. When comparing such a phase behavior with that of the C(16)mimCl/H(2)O binary system, an additional V(2) phase is identified and could be attributed to the different affinities of C(16)mimCl to EAN and water. Higher temperatures induce smaller lattice spacing for the LC phases, which may be due to the softening of the solvophobic chains of C(16)mimCl molecules. Both the imidazolium ring structure and alkyl chain of C(16)mimCl molecule are proved to play important roles for the LC phase formation. Dissipative particle dynamic simulations are also carried out at room temperature, and the obtained intuitive three-dimensional (3D) models can help us better understand the self-assembled structures, which are considered to be supplements for the experimental results.
The Journal of Physical Chemistry B 02/2009; 113(7):2024-30. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The supramolecular ionic self-assembly (ISA) strategy has been used to construct the long-range ordered hierarchical aggregates from the complexes of 1-adamantanamine hydrochloride (AdCl) and sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT). The formed AOT-Ad complexes have been proved to possess a composition of equal molar ratio and a hexagonal columnar structure with Ad blocks as the core and AOT outside. More interestingly, the length, width, and thickness of the aggregates are on the order of milli-, micro-, and nanometer, respectively, and can thus be taken as one type of organic nanobelt. Such nanobelts are plastic and stable to resist breakage even bent to a circle, which makes them useful in the fields of novel nanomaterial fabrication. In addition, the ISA process of this aggregate can be tuned by including Ad blocks in beta-cyclodextrins to form a supramolecular complex, which is comparatively stable in the water and expected to self-assemble into some other ordered structures.
The Journal of Physical Chemistry B 07/2008; 112(24):7191-5. · 3.70 Impact Factor
-
ChemPhysChem 03/2008; 9(2):249-52. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Self-assembly vesicles have been made from a cyclodextrin (CD) supramolecular complex, which is cooperatively formed with natural beta-CD, 1-naphthylammonium chloride (NA), and sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) by weak noncovalent interactions. In the complex structure, a NA molecule is included inside a beta-CD molecule while it is coupled with an AOT molecule on one side. The supramolecular structure and morphology of the vesicles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. The mechanism of vesicle formation and transition is discussed along with the data obtained from induced circular dichroism (ICD) and UV/visible spectroscopy, polarized optical microscopy (POM), and (1)H NMR spectroscopy. Both the fabrication and the transition of vesicles are controlled by the inclusion equilibria and the cooperative binding of noncovalent interactions, which include the "key-lock" principle, electrostatic interactions, pi-pi stacking, and amphiphilic hydrophobic association.
Chemistry 02/2007; 13(32):9137-42. · 5.93 Impact Factor
